Problem: $ { {-1} \times \left[\begin{array}{r}{1} \\ {4} \\ {2}\end{array}\right] = {?} } $
Answer: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{r}{-1}\times{1} \\ {-1}\times{4} \\ {-1}\times{2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{r}{-1} \\ {-4} \\ {-2}\end{array}\right]}$